STAR specifies two methods for attachments.

These methods are compatible with each other as the soap envelope, binary data encoding, and HTTP transport are the same. MTOM is supported by newer frameworks, and treats the binary data as if they were just part of the XML data. SOAP with Attachments is the old specification but is still used by many older frameworks. STAR RECOMMENDS that implementations use MTOM as it provides a cleaner programmatic interface for working with attachments. Since attachments are an advanced concept that not every implementation needs, it is considered a STAR Level 2 requirement. Also due to the critical nature of most attachments they need to be Reliable ans Secure so use of WS-ReliableMessaging is required.

The STAR attachment element is defined to allow transporting non-XML data. All internal attachments are encoded as the xsd:base64 data type. External attachments, those that reside on a server, can be communicated using the provided URL identifiers.

	Note
	STAR also recommends the use of the Large File BOD to handle transmittal of files that may normally be too large to provide as an attachment. The Large File BOD allows for the specification of files to be transmitted in chunks and then re-assembled once they are received.

Binary attachments are to use the MTOM standard or the backwards compatible SOAP with Attachments specification if MTOM is not supported by the tooling framework. The use of DIME attachments is not supported.

	STAR Level 2 Rule
	STAR2013: Attachments MUST use MTOM attachments or SOAP with Attachments. MTOM attachments are RECOMMENDED over SOAP with Attachments. STAR2014: The use of DIME attachments MUST NOT be used.

MTOM allows an efficient way for binary data to be included in a SOAP envelope with out the need for encoding that data in an XML wrapper. MTOM and SOAP with Attachments make use of the Multipart-Mime encoding mechanism of the HTTP transport to send the data. Frameworks that support MTOM and SOAP with Attachments then can retrieve the attachments via the reference ID.

For these attachments, this element points to the attachment that resides outside the SOAP Envelope.

	Note
	This element is intended primarily to support non-XML data that is not part of a BOD; for example, transactions presented in comma-separated files. BODs that embed non-XML data, such as an image, define their own method of encoding or referencing the binary data.